1. Field of the Invention
The present invention applies to radio communications systems in which several remote terminals communicate voice or data with several different base stations and, in particular, to such a system in which the base stations share a broadcast channel with the other base stations.
2. Description of the Prior Art
Mobile radio communications systems such as cellular voice radio systems typically have several base stations in different locations available for use by mobile remote terminals, such as cellular telephones or wireless web devices. Each base station typically is assigned a set of frequencies or channels to use for communications with the remote terminals. The channels are different from those of neighboring base stations in order to avoid interference between neighboring base stations. As a result, the remote terminals can easily distinguish the transmissions received from one base station from the signals received from another. In addition, each base station can act independently in allocating and using the channel resources assigned to it.
Such radio communications systems typically include a broadcast channel (BCH). The BCH is broadcast to all remote terminals whether they are registered on the network or not and informs the remote terminals about the network. In order to access the network, a remote terminal must normally tune to and listen to the BCH before accessing the network. A remote terminal will typically scan a range of likely frequencies when it wants to access the network until it finds the strongest BCH, it will then use the information in the BCH to access the network. Just as with the traffic channels, the broadcast channels BCH are typically different for each base station. This reduces interference between adjacent base stations and allows the BCH channel to be selected to optimize transmission quality for the radio environment at each base station's location.
Separate broadcast, control and access channels allow great flexibility in designing a wireless radio network of base stations and channel allocations. However, each channel that is set aside for broadcast, control or access purposes cannot be used for traffic. When the number of channels is limited in comparison to the demand for traffic, it is preferred to maximize the traffic usage of all of the system's radio capacity. The present invention allows many base stations to share a single broadcast channel. This allows less of the channel resources to be dedicated to the broadcast channel and more of the channel resources to be dedicated to traffic.